Brake mechanism



Dec. 21, 1943. w, R SPILLER ET AL 2,337,069

BRAKE MECHANISM 2 Sheets-Sheet 1 Filed April '7, 1941 \gmm Dec. 21,1943. w. R. SPILLER EI'AL BRAKE MECHANISM Filed April '7. 1941 2Sheets-Sheet 2 4 5 Wm i w gnwmw N RM W 27 $7 acteristlcs.

Patented Dec. 21, 1943 BRAKE MECHANISM William R. Spiller, Dayton,

Alden and Ralph K. Super, Detroit,

Ohio, and Herbert W.

Mich, as-

signors to The Timken-Detroit Axle Company, Detroit, Mich, a corporationOhio Application April '1, 1941, Serial No. 387,314

24 Claims.

The present invention relate to brake mechanisms, and more particularlyto internal expandins drum brakes for automotive vehicles, although itis not limited to such use.

In a conventional brake, the brake shoe is pivoted on a fixed anchor pinand rocks about a definite axis, between engaged and disengagedpositions. Although in such a brake ther is a direct line relationshipbetween the force applied and the braking torque developed, it is opento the disadvantage that through a phenomenon known as toe grab, orself-locking, the shoe will often grab and cause uneven braking, and/oruneven wear of the brake lining. Circumferential extent or span of thelining in such brakes must be held to small limits; the anchor pinmounting must be maintained closely adjacent the drum; and thecoeilicient of the lining must be kept comparatively low to avoid toegrab and sell-locking o! the shoe. Each of these factors serves todecrease the braking power or torque capacity of the brake.

In the .Servo brakes of the prior art, a primary shoe is mounted forfloating movement and is linked to a secondary shoe, which in turn ispivoted on an anchor pin. The braking torque of such brakes is greaterthan a. conventional brake of given size, but they are open to seriousdisadvantages. The majordifllculty of this brake is that it is notcompletely controllable under'all conditions. For" one thing, a releaseof, or reduction in, pedal pressure is not always reflected as acorresponding cessation of, or reduction in, braking torque, with theresult that the brake is not altogether reliable in operation.

In Hayes et al. Patent No. 2,208,293, granted July 16, 1940, there isdisclosed a brake mechanism embodying a shoe assembly mounted forpivotal and sliding movement and designed to overcome the toe grabbingdefect of conventional pivoted shoes, and to also permit the brakingpower to be increased and an appreciable degree of self-energizingaction achieved, by shitting the anchor pin inwardly toward the axis ofthe brake drum, and increasing the degree to which the lining at the toeend of the shoes is extended.

Although the patented structure represents a substantial advance in theart over the other brake mechanism of th prior art, from the standpointsof construction and' operation it is notsltogether successful and fallsshort or a brake having all of the desired operating char- The Hayes etal. brake, by reason or the slotted shoe end construction, is subject tostructural distortion or failure when excessive braking torques areimposed upon the mechanism, and also, because the braking torque istaken solely at one end of each shoe, the increased braking torque dueto anchor pin location is achieved ior only one direction of rotationfor each shoe. When the drum rotation is reversed the shoe functionssubstantially thesame as the trailing shoe of a conventional anchoredbrake shoe assembly. Therefore, the improvements made by Hayes et al.are only available for one direction of rotation of each shoe.

It is the major object of this invention to provide a brake mechanismhaving all of the advantages of the Hayes et al. brake, and in additionpossesses highly important structural features which render it extremelyrugged and also give it highly improved operating characteristics.

Another important object is to provide a novel multi-shoe brakemechanism which is so designed that toe grab is eliminated; the shoesare floatingly mounted for movement into full engagement with the drum;and each shoe possesses substantially the same braking characteristicsin both directions of rotation of the drum.

A further object is to provide a brake mechanism embodying means forsupporting each shoe for floating movement toward and away from the drumin such manner that, when either end of the shoe is engaged with thedrum, the opposite end may move toward and bring the full area of thelining into engagement with the drum.

A further object is to provide a novel mount for a floating brake shoe,embodying an inclined abutment assembly at each end of the shoe, forimparting predetermined braking characteristics to the shoe when forwardor rearward brake torquing reactions are applied thereto.

The invention also aims to provide a brake mechanism embodying a novellever assembly designed to opcrably support each shoe for floatingmovement, and to also apply actuating iorces to the central portion ofthe shoe.

Another object is to provide a brake shoe mounting which anchors theshoe at both ends and yet permits i'ree pivotal movement about each endas well as free translational movements of each end oi the shoe towardand away from the drum. I

A further object is to provide a brake mechanism in which each shoe issupported on two anchor pins, symmetrically located with respect to thecenter of pressure of the resultant forces acting on the shoe, the an hr pins being op mechanism, and also a novel able to impart similaroperating characteristics to the shoe in both directions of drumrotation.

Further objects are to provide novel adjust, ing means, novel levelfulcrum means, novel anchor means, and to generally improve and refineother features of the brake mechanism of the prior art, which willbecome apparent as the specification proceeds in conjunction with theannexed drawings.

Figure 1 is a fragments] elevatlonal view of a brake mechanism embodyingthe invention, with the brake drum and certain other parts broken awayto more clearly illustrate the construction involved;

Figure 2 is a vertical sectional view taken substantially alon line I-2of Figure 1, looking in the direction of the arrows;

Figure 3 is a fragmental sectional view through the brake shoe and leverpivot assembly, taken substantially on the line 33 of Figure 1:

Figure 4 is a fragmental sectional view taken on the line 4-4 of Figure1;

Figure 5 is a fragmental sectional view of a modified form of brakeanchor adjusting mechanism which may be used in the construction shownin Figure l, and also forming part of the invention; and

Figure 6 is a sectional view taken substantial- 1y along the line 66 ofFigure 5.

With continued reference to the drawings, wherein like referencecharacters have been employed to designate like parts throughout theseveral views thereof, the brake mechanism broadly comprises a brakedrum'A, a pair of brake shoes 16 and a hydraulic piston and cylinderassembly 0, although it is to be understood that a cam or any well-knownform of link construction may be used instead of hydraulic or pneumaticpressure for actuating the brake.

The brake assembly is carried by a foundation plate ill. havin a centralopening Ii desi ned to fit over any suitable form of axle constructionand has a plurality of openings I! through which fastening screws orrivets are inserted to secure the foundation plate to a flange on theaxle. Plate i is flanged to provide a dirt-excluding lip I I and a brakedrum I4 is mounted for rotation on the wheel or hub assembly incooperative relationship with lip l! in well known manner. The brake ofthe invention embodies both a novel floating mount for the brake shoes,which imparts improved braking characteristics to the p sure app yinlever assembly. The novel floating brake mount will first be described.

Rigidly secured to backing plate ill is a pair of anchor pins I! and It.Pin i is provided with large and small diameter concentric Journalportions I1 and II, respectively. and an intermediate eccentric portionil. l The large diameter Journal portion is pulled into tight engagementwith plate II by means I! and a spacer member 23. The latter is providedwith a flange fl, and is located in a cupped portion II formed in thefoundation plate. Spacer II is preferably riveted to the foundationplate, so as to provide a rugged Journal for pin II.

Pin ii is provided with a squared end 21. so that by loosening nut 2|the pin may be engaged by a wrench and turned to rotate the eccentric,and thereby 'adlust the brake in a manner to be hereinafter pointed out.

Upper pin II is provided with ashoulder II, which is pulled into tightengagement with a reof a nut Ii, a lock washer ass-1,000

inforcing plate Ii, secured in turn to backing plate II by means ofrivets 32. Pin II is provided with a smooth Journal portion 83. Theshoulders of pins II and it are preferably serrated and cooperate withserrations on backing plate ill and plate II (not shown) for preventingthe pins from rotating.

Anchor pins l6 and it constitute the sole support for the shoe and leveractuating mechanism and since the two pairs of actuating pins supportthe two shoes in exactly the same manner, the right-hand shoe, which isof identical construction, has not been illustrated (Figure 1) thedescription of the left-hand shoe clearly constituting a full disclosureof the invention.

The brake shoes may be of any desired constructlon and each embodies acylindrical portion it having brake lining material 36 secured theretoin any suitable manner, as for instance by rivets or the like, and maybe applied in two or more sections. The shoe has a central web or flange31 provided at its opposite ends with abutment faces 38 and 39, whichcooperate with link or abutment members ll and 42, respectively.

The abutment members are carried by the anchor pins, and by reason oftheir novel construction, they directly absorb the braking torquereaction of the drum in both directions of rotation. Abutment member llis pivoted upon eccentric portion iii of anchor pin it, so that byrotating the anchor pin the abutment member is correspondingly actuatedto advance or retract the lower end of the shoe with respect to thedrum. The upper abutment member 42 is pivoted upon anchor pin it. v

The coactin faces of the abutment members are comparatively long, so asto avoid high localized pressures, and to also insure pivotal movementof the abutment members in response to the application of drum reactionforces thereto and prevent the abutment members from swinging around andlocking the shoes in ensaged position.

Preferably resilient means is employed to constantly maintain the endsof the shoes in engagement with their abutment members when the brake isreleased, as shown in figure l. A tension spring H has its opposite endshooked into openings 45 and 45 in the brake shoe flange, and is providedwith two The intermediate tends around the outside of abutment member II. The spring constantly urges face 3| of the brake shoe towardengagement with abutment member 4 i, so that no independent pivotingmovement of the latter can occur. By acting along a line normal to faceIii, there is no tendency for-thespring to slide the shoe end across theface ,of member I. A somewhat dlii'erent spring arrangement is employedfor maintaining abutment member If in engagement with the upper end ofthe brake 8h. will be the description of the lever'assembly.

Although the brake shoes may. be actuated toward the brake drum by anysuitable actuating mechanism, we preferably cm by the following novel 1er assembly because t maintains accurate con 01 over all movement ofeach shoe, eooperates with the abutment members to guide the shoe foraccurate movement toward and away from the drum, and also appliesactuating forces substantially at the mid-portion of the slice, so as toeffect a substantially uniform distribution of braking pressure.

A pair of levers II and II, of substantially idencoiled portions 41 andI. portion I! of the spring 44 exdescribed in coniunction with.

tical shape, are secured together in spaced parallel relationship bymeans of spacer pins 53, 54 and 55. Each pin is provided with anenlarged central portion providing opposed shoulders against which thelevers are tightly held in place and by riveting ends of the pins.

Lever isiournalled on the large diameter portion ll of anchor pin l5,while lever 52 is Journalled on small diameter portion 18. The leverassembly is detachably secured in place on the lower anchor pin by meansand a split ring 51, which is sprung into a groove in the anchor pin. 7

Each lever, adjacent its upper end, is provided with an elongated slot58 for clearing the upper anchor pin. The ends of slot 58 in lever 5|cooperate with the upper anchor pin to limit extreme' movement of thelevers in both directions. As shown in Figure i, the brake shoe is inreleased position. and the left-hand end of slot 58 in lever Si isengaged with the upper anchor pin.

The upper end of the lever assembly is maintained in cooperativerelationship to the foundation plate by means of a washer GI and a snapring 62 sprung into a groove in anchor pin it.

The upper end of the lever assembly is accordingly freely rockable in aplane normal to the upper anchor pin, but is restrained against movementaxially of the pin. As seen in Figure 2, a shoulder 63 on the pinrestrains link member 42 against movement to the right, which in turnrestrains the lever assembly against similar movement, and the snap ringassembly inst described prevents movement of the assembly in theopposite direction.

Each brake shoe is constantly urged toward disengaging position by meansof a novel retracting spring assembly, which also constantly urgesabutment face 39 of the brake shoe toward engagement with its abutmentmember 42. A

, short link member 65 has one end thereof hooked in at bore 88 in thebrake shoe web, and is provided at its free end with an eye 81. Somewhatsimilar link member 68 is hooked into an opening 89 in the upper end oflever 5|, and is provided at its free end with an eye H. A tensionspringI2 is hooked into eyes 81 and H at one end and at the other end ishooked into the corresponding eyes of the opposite brake shoe and leverassembly. Spring 12, acting through links 85 and 80, accordingly,constantlyurges the brake shoe away from the drum and toward theengagement with its abutment member 42, and also urges the leverassembly into retracted position, in engagement with pin l6. Link 88confines the pull of spring 12 upon link 65 to a direction substantiallynormal to face 19, with the result that there is no tendency to slidethe upper end of the shoe across the face of member 42.

The lever assemblies may be actuated by hydraulic, pneumatic ormechanical means of any desired character, it only being necessary tospread the upper ends of the lever assemblies to actuate the brake. Inthe present instance, however, we have illustrated a well-known type ofhydraulic mechanism embodying a cylinder I6 having a piston in each endthereof. Piston rods 15 are provided with forked portions 18, which fitover, and fulcrum against, the upper spacer pin 55 of each leverassembly.

It is accordingly apparent that, when pressure is applied to cylinder14, rod 15 will move outwardly and cause the lever assemblies to fulcrumabout lower anchor pins I! as axes. Rocking movement of the leverassembly is transmitted to of a washer 56 mitting the shoe toautomatically find a seat on the drum in full surface engagementtherewith.

J ournalled in a bushing I8 in brake shoe flange 3! is a trunnion memberI! having a pair of slots 8| and 82 formed therein (Figure 3). Levers 5iand 52 are each provided with a straight edge 83, which slidably coactswith the grooves in the trunnion member. The grooves, being locatedadjacent the diameter of the trunnion, provide long bearing surfaces ofadequate area to sustain the loads imposed by the levers, which areconstantly maintained in full surface engagement with the bottoms of thegrooves.

The lever assemblies are accordingly operative to apply forces to thecentral portion of the brake shoe through trunnion member 19, and at thesame time individual lever members may freely slide relatively to theshoe in the trunnion member slots, thereby permitting any self-aligningaction to freely take place. In order to further insure free slidngmovement of the shoe web between the latter, slightly raised bosses illand 85 are provided on the brake shoe web adjacent abutment faces 38 and39, respectively, and also a circular boss 86 is formed on the webadjacent trunnion member 19. Working clearances are provided between thebosses and the brake shoe flange, but the parts fit sufficiently closeto insure accurate guiding of the shoe.

The novel brake mechanism of the invention embodies what may be termed ashifting anchor for each shoe. For instance, if the brake is actuatedwhen the drum is rotating in one direction, the drum reaction is takenby one set of anchor pins, and when the direction is reversed the drumreaction is taken by the other pair of anchor pins. Also, the mechanismpossesses a further highly desirable function of so functioning thateach shoe functions as a leading shoe in both directions of drumrotation, with the result that controlled degrees of self-energizingaction may be secured.

Operation Assuming that the drum is rotating counterclockwise,(Figure 1) and hydraulic 'or pneumatic pressure is applied to cylinder14, piston rod 15 moves outwardly, and rocks the lever assemblycounterclockwise about the axis of anchor pin l5. This action, throughtrunnion it, forces the brake shoe outwardly against the action ofspring 12 and spring 44, which constantly urges the abutment faces ofthe shoe toward their links. The resulting substantially horizontalmovement of the shoe causes slight clearances to develop between theshoe abutment faces and their links. Whether or not the clearancesdeveloped are equal is immaterial because, as soon as contact of theshoe is made with the drum, the shoe may rock slightly about the axis oftrunnion 19* and bring its full surface into engagement with the drum,thereby effectively avoiding "high spots" or areas of high localizedpressures, and insuring long life of the brake lining.

As soon as the shoe has been brought into engagement with the drum asjust described, the braking torque reaction carries the shoe a slightangular distance, so as to tightly engage its abutment face 38 withabutment member 4i, and if for any reason a clearance exists betweenthem localized pressure at either member If is automatically rocked soas to bring them into full surface engagement.

Under the conditions just described, and considerlng the shoe shown inFigure 1 alone, the brake is fully applied and the drum reaction istaken solely by lower anchor pin i 5. A slight clearance exists betweenthe upper end of the brake shoe and its abutment member 2, because theoutward movement of the lever in combination with the drum reaction hasseparated these surfaces against the action of spring 12. The oppositeshoe (not shown) functions-in exactly the same way for clockwiserotation of the drum as the illustrated shoe for counterclockwiserotation, since the levers are fulcrumed the same side of the axis ofrotation.

In view of the foregoing, it is apparent that, if the upper or lower endof the shoe should first engage the drum during the initial stage ofbrake operation, it will merely result in the shoe being bodily rockedinto full surface engagement with the drum, and there is accordingly nopossibility of toe grab" or greater lining wear at one end than theother.

The brake of the invention is accordingly free from all of thedisadvantages of the prior art, possesses the advantages over theslotted shoe type of brake of applying the pressures approximatelycentrally of the brake shoe, and in addition each shoe functions as aleading shoe in both directions of rotation, as will now be pointed out.

Assuming that the drum is rotated in the opposite direction, namely,clockwise as viewed in Figure 1, and the brake actuated as before, thedrum reaction torque forces the brake shoe'angularly in a clockwisedirection, so as to bring its surface 39 into tight engagement withabutment member 42. This transmits all of the braking reaction forcesapplied to the shoe to anchor pin IS. The bodily movement of the shoe ina clockwise direction in response to the torque reaction causes anincreased clearance to develop between abutment surface 38 and abutmentmember it, against the action of spring 41. This removes anchor pin itfrom the sphere of action entirely, and the shoe may be regarded duringthis operation as being floatingly anchored to pin ll alone. Inother-words, the eifectual anchor for the brake shoe has been shifted ortransposed, through a reversal of rotation of the drum, from pin I I topin it, and all of the advantages of the leading shoe, which includes adesirable degree of self-energization, realized for both directions ofdrum rotation. 5 7

It is also observed that during the braking operation the braking forcesare constantly applied to the mid-portion of the shoe, thereby avoidingend: insuring uniform pressure distribution: and at'the same timepermitting either end of the shoe to move in.- wardly and outwardly, soas to compensate for a slightly out-of-round brake drum.

It is, of course, understood that the shoe on the opposite side of theaxis from the'shoe illustrated functions in exactly the same way but atdifferent times; namely, when the drum is tototing clockwise as Justdiscussed, the shoe opposite the one shown will transmit the brakingtorque reaction to lower anchor pin II. and when the drum is rotating inthe oppositedirection it will transmit the braking torque reaction toupper pin ii. In either event, both shoes the operating characteristicsof a leading shoe in either direction of rotation of the drum, by reasonof the transfer of the braking torque reaction forces from one set ofanchor pins to the other upon reversal of drum rotation. Upon conclusionof the braking operation, the pressure is released from cylinder 14, andsprings 44 and 12 return the shoes and levers to inoperative position,and there is no tendency, as in the shoe brakes of the prior art, forthe disengaging operation to be delayed.

In order to simplify the disclosure, the foregoing description of theconstruction contains no mention of critical angles and dimensions ofthe parts used in the brake. .The various factors which influence theoperating characteristics of the brakes will be taken up separately asfollows:

Brake lining span In the prior pivoted shoe brakes, it is necessary toso limit the span of the lining as to seriously reduce the braking power01' the mechanism. If the lining were carried too far at the toe end,serious toe grab would occur, and if it were carried too far under theheel of the shoe, little braking action would be obtained from thatportion of the lining.

In the present construction the whole shoe is a mounted for bodilytranslational movement, and the forces are applied approximatelycentrally of the shoe, so that the lining may be carried as far as ispracticable without encountering the difficulties from shoe grab, and atthe same time all parts of the lining bear with equal force against thedrum. In the brake illustrated the angle E, indicating the span of thelining, is approximately 1.14 degrees, which has been found verysatisfactory in actual operatic However, it is to be understood that theangular extent or span of the lining may be increased or decreased withrespect to this value without departing from the spirit of theinvention.

Abutment face inclination For either direction of drum rotation thereare three forces acting upon the shoe; namely, (1) the actuating force Pacting through trunnion 19 substantially at the mid-point of the shoe,and directed substantially longitudinally, Figure 1; (2) the thrust ortorque reaction Q: or Q: acting at to the particular anchor pin 15 orii) involved; and (3) the resultant drum reaction R passing through theintersection X of P and Q.

The force diagram may be solved vectorially in well known manner tolocate point X. As shown in Figure 1, abutment faces 38 and of the shoeare disposed at right angles to lines Q1 and Q2, respectively, drawnthrough the axes of the anchor p and intersection x of lines P, R, Q1and Q3. iAS seen in Figure l, the resulting arrangement is perfectlysymmetrical.

The point X is shown in the position illustrated in the drawings only byway of illustration of the theory of the brake, and it is to beunderstood that in practice its location will depend upon the coemcientof friction of the lining.

From the foregoing it is apparent that the invention is not limited tothe abutment face inclination disclosed, because they will vary inaccordance with the location of the anchor pins, but in any event willbe disposed normal to lines containing the anchor pin axes and the pointof intersection of the three forces acting upon the shoe Anchor pin.placement In the brakes of the prior art it has been necessary to locatethe anchor pins very close to the inner surface of the drum toavoidself-locking dlfllculties. especially those which occur through toegrab.

In the present construction no difllculties with the phenomena of toegrab or self-locking of the shoe are possible, and therefore the anchorpins may be moved inwardly to achieve an appreciable increase in brakingpower of the mechanism through an additional self-energizing'action.

Inthe construction illustrated, pin I6 is located slightly closer to theaxis than pin ii, in order to accommodate the actuating mechanismdisclosed. However, since the braking power is maintained of constantvalue so long as the pins are maintained on reaction lines Q1 and Q2,the braking power will be the same when the drum is rotatingcounterclockwise as it is when it is rotating clockwise. Accordingly,the distances of the two anchor pins from the drum axis may he madeequal or varied through substantial ranges to suit any particular layoutbecause in order to achieve satisfactory operation it is only necessaryto locate the pins along the lines Q1 and Q2, and so shape abutmentfaces 38 and 39 as to be disposed normal to lines Q1 and Q2, and thiswill produce equal braking effects for both directions of drum rotation.

Brake cdiustment If after the brake has been in use for some time thelining becomes so worn as to introduce an undesirable clearance betweenthe lining and the drum. each nut 2| is loosened and pin it rotatedsufllclently to cause the eccentric portion, acting through link II, toadvance the shoe toward the drum and compensate for the lining wear:Nuts 2| are then tightened and the adiustment is complete. As seen inFigure l, rctation of the eccentric in either direction will advance theshoe toward the drum, but the one shown is preferably rotatedcounterclockwise, and the opposite one rotated clockwise to advance theshoe toward the drum.

In Figures 5 and 6 there is illustrated a modifled construction foradjusting the lower anchor pins, also forming part of the invention.With continued reference to these figures, the parts which are similarto those of the construction Just described will be given the samenumber with the subscript a.

In this form 01' the invention a modified form of anchor pin 16a isused, each of which extends through an elongated slot 9! in foundationplate 10a.

Levers Bio and 52a, together with abutment member lla, are pivoted on anenlarged con centric cylindrical portion 92 of each anchor pin lie. Theshoulder formed by enlarged portion 92 is adapted to be pulled intotight engagement with plate Ilia by means of a nut, a lockwasher GI, andan enlarged block member 9! fitting over each anchor pin. As seen inFigure 5, each block 95 is provided with a portion depending below theanchor pins.

An adjusting member 81, having a central hexagon shaped portion, isprovided with oppositely threaded portions 98 threaded into member 95.

By loosing nuts 93, so as to free the anchor pins for sliding movementin slots 8|, member 81 may be rotated to move blocks 95 toward and awayfrom each other so as to increase or decrease the clearance that existsbetween the brake lining and the drum. When the adiustment is completednuts 93 are then tightened to permanently lock the anchor pins in theirnew positions.

The term brake shoe in the appended claims is intended to embrace theshoe illustrated embodying the shoe proper and lining 36, but it is tobe understood that it also covers brake shoes having an integral brakingface.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States LettersPatent is:

1. In a brake mechanism, a brake drum; a support mounted in cooperativerelationship to said brake drum; a brake shoe carried by said supportand movable toward and away from said brake drum; means for forcing saidshoe toward said drum; an abutment member carried by said support andcooperating with one end of said shoe for restraining it againstrotation in response to rotation of said drum in one direction; a secondabutment member carried by said support and coacting with the other endof said shoe for restraining it against rotation in response torotation-of said drum in the opposite direction; one of said abutmentmembers being located closer to the axis of the drum than the other, andsaid brake shoe having flat faces adjacent its ends cooperating withsaid abutment members, said abutment members each permitting free,substantially radial outward movement of the ends of said shoe, andslight bodily rocking of said shoe about either of said abutment membersas a fulcrum, so as to insure full surface engagement of the shoe withthe drum when the latter is rotating in either direction, the flat facesof said brake shoe being inclined differently from the othersufliciently to compensate for the differential placement of saidabutment members with respect to said axis, and efiect similar brakingcharacteristics in both directions of drum rotation.

2. The brake mechanism defined in claim 1, wherein said shoe is providedwith a flat, substantially non-radial face at each end thereof :oactingwith flat faces on said abutment memers.

3. In a brake assembly, a foundation plate; a pair of anchor pinscarried by said plate and spaced apart circumferentially; a brakeactuating lever mounted for pivotal movement on one of said pins; abrake shoe disposed in operative relationship with respect to said plateand being provided adjacent each end with an abutment face disposed inproximity to said anchor pins; an abutment member pivotally mounted oneach of said anchor pills and coacting with the abutment faces of saidbrake shoe, and being free to rock into various positions in response toforces applied thereto; means for rocking said lever about said one pin;and means for transmitting forces from said lever to said brake shoe.

4. In a brake assembly, a foundation plate; a pair of anchor pinscarried by said plate and spaced apart circumferentially; a brake,actuating lever mounted for pivotal movement on one of said pins, abrake shoe disposed in operative 5 relationship with respect to saidplate and being provided adJacent each end with an abutment i'aceadjacent said anchor plus; an abutment member pivotally mounted on eachor said anchor said brake shoe. and being tree to rock into variouspositions in response to forces applied thereto: means for rocking saidlever about said one pin: and means for transmitting iorces from saidlever to said brake shoe. said abutment races being inclined with r pectto radii intersecting said anchor pins so as to impart predeterminedbraking characteristics to said brake shoe when it is engaged with oneof said pivotally mounted abutment members.

5. In a brake assemb ri foundation plate; a pair 01' anchor pins carriedby said plate and spaced apart circumi'erentially; a pair of brakeactuating levers mounted 1 here constituting the sole means to:transmitting brake 9. In a brakemechsnlsm. a support; a lockable membercarried by said support: a pair of spaced levers i'uicrumed on saidmember. said member also having an eccentric portion intermediate saidlevers; and a brake shoe abutting element fitting over said eccent icportion, and adapted to be ada brake drum mountv said support; a brakeby said support and mounted for movement toward and away from said brakedrum; a lever pivotally mounted on said support lever and said brakethus.

13. In a brake, a brake drum;

vlnl, abutment races cooperating therewith to restrain 15. In a brake,

brake drum; said pins being disposed to the same side of a planecontaining the drum axis; a rigid brake shoe disposed in operativerelationship with respect to said support and located to the same sideof the drum axis as said pins and being provided adjacent each end withan abutment face disposed in proximity to said anchor pins; an abutmentmember pivotally mounted on each of said anchor pins and coacting withthe abutment faces of said brake shoe, and being free to rock intovarious positions in response to forces applied thereto by said shoe; apivoted actuating lever for rocking said shoe; and means fortransmitting forces from said lever to said brake shoe adjacent themid-portion thereof.

16. In a brake, a support; fulcrum means carried by said support; alever assembly pivotally mounted on said fulcrum means and comprising apair of levers secured together in spaced apart relationship; a brakeshoe mounted on said support and having a web portion slidably disposedbetween said levers; forces from said lever assembly to said shoecomprising a force transmitting member having pivotal movement upon alarge area curved surface on the web of said brake shoe, and havingsliding movement upon a large area flat surface on said lever assembly.

17. In a brake a support; a brake drum mounted for rotation adjacentsaid support; a

brake shoe carried by said support and mounted for movement toward andaway from said brake drum; a lever pivotally mounted upon said supportand having its free end disposed adjacent one end of said brake shoe;means for retracting said brake shoe and lever, comprising a tensionspring; a link connecting one end of said tension spring to the free endof said lever assembly, and a second link connected to said spring endand anchored to one end of said brake shoe.

18. The brake defined in claim 1'1, wherein said links are disposed atan angle of approximately 90 to each other and the line of action ofsaid spring substantially bisects said angle, whereby the action of thespring upon said brake shoe is restricted to a direction substantiallynormal to said first link.

19. In a brake, a support; a brake drum mounted for rotation adjacentsaid support; a

pair of substantially axially directed anchor pins carried by saidsupport and disposed in circumferentially spaced relationship; anabutment member mounted for free rocking movement upon each of saidanchor pins and having a substantially flat bearing face extending asubstantial distance in either direction from a line normal to saidbearing face and passing through the axis of said anchor pins; abutmentfaces adjacent the ends of said brake shoe having areas substantiallycoextensive with the area of the bearing faces of said abutment membersand means for transmitting operable to coact in full surface engagementwith one abutment member when the brake is applied in one direction ofdrum rotation, and to coact in full surface engagement with the otherabutment member when the drum is rotating in the other direction; andlever means for applying braking forces to said brake shoe intermediateits length.

20. The brake construction defined in claim 19, wherein said bearingfaces, measured in a direction normal to the drum axis, each have alength materially greater than the distance of said bearing faces fromthe axis of said anchor pin, for insuring free rocking of said abutmentmembers in response to the application of braking reaction forcesthereto by said shoe.

21. The brake construction defined in claim 19, together with means foradjustably decreasing the circumferential spacing of said abutmentmembers, to compensate for the effect of brake lining wear.

22. The brake construction defined in claim 19, wherein one of saidabutment members is pivoted upon an eccentric portion provided on itspin, and the latter is mounted for adjustment into a plurality ofangular positions, for adjustably varying the circumferential spacing ofsaid abutment members, to compensate for the effect of brake liningwear.

23. In a brake mechanism, a brake drum; a support mounted adjacent saidbrake drum; a pair of circumferentially spaced anchors on said support;a brake shoe assembly disposed between said anchors and having abutmentmeans cooperating therewith to restrain said shoe against rotation inresponse to braking forces, and operable to permit either end of saidshoe assembly to move toward or away from said drum; a brake shoeactuating lever assembly pivoted adjacent one of said anchors; means fortransmitting forces from an intermediate portion of said lever assemblyto an intermediate portion of said shoe assembly, comprising a forcetransmitting member having a large area curved surface cooperating insurface engagement with a large area curved surface means on one of saidassemblies, and also having a large area fiat surface cooperating insliding engagement with a large area fiat surface means on the otherassembly; and means for rocking said lever.

24. The brake mechanism defined in claim 23, wherein said lever assemblycomprises a pair of spaced levers and said brake shoe comprises a webdisposed between said levers, and said flat surface means comprises afiat surface on each of said levers, and said curved surface meanscomprises a curved surface on said brake shoe web.

WILLIAM R. SPIILER. HERBERT W. ALDEN. RALPH K. SUPER.

